![]() ![]() They are important constituents of several key enzymes and play important roles in various oxidation-reduction reactions. The essential heavy metals exert biochemical and physiological functions in plants and animals. Biological factors such as species characteristics, trophic interactions, and biochemical/physiological adaptation, also play an important role. It is also affected by chemical factors that influence speciation at thermodynamic equilibrium, complexation kinetics, lipid solubility and octanol/water partition coefficients. Their bioavailability is influenced by physical factors such as temperature, phase association, adsorption and sequestration. Heavy metals are also considered as trace elements because of their presence in trace concentrations (ppb range to less than 10ppm) in various environmental matrices. Inadequate supply of these micro-nutrients results in a variety of deficiency diseases or syndromes. It has been reported that metals such as cobalt (Co), copper (Cu), chromium (Cr), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), nickel (Ni), selenium (Se) and zinc (Zn) are essential nutrients that are required for various biochemical and physiological functions. Industrial sources include metal processing in refineries, coal burning in power plants, petroleum combustion, nuclear power stations and high tension lines, plastics, textiles, microelectronics, wood preservation and paper processing plants. Natural phenomena such as weathering and volcanic eruptions have also been reported to significantly contribute to heavy metal pollution. Environmental contamination can also occur through metal corrosion, atmospheric deposition, soil erosion of metal ions and leaching of heavy metals, sediment re-suspension and metal evaporation from water resources to soil and ground water. Īlthough heavy metals are naturally occurring elements that are found throughout the earth’s crust, most environmental contamination and human exposure result from anthropogenic activities such as mining and smelting operations, industrial production and use, and domestic and agricultural use of metals and metal-containing compounds. Environmental pollution is very prominent in point source areas such as mining, foundries and smelters, and other metal-based industrial operations. Reported sources of heavy metals in the environment include geogenic, industrial, agricultural, pharmaceutical, domestic effluents, and atmospheric sources. Also, human exposure has risen dramatically as a result of an exponential increase of their use in several industrial, agricultural, domestic and technological applications. In recent years, there has been an increasing ecological and global public health concern associated with environmental contamination by these metals. With the assumption that heaviness and toxicity are inter-related, heavy metals also include metalloids, such as arsenic, that are able to induce toxicity at low level of exposure. Heavy metals are defined as metallic elements that have a relatively high density compared to water. ![]() This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity. Environmental Protection Agency, and the International Agency for Research on Cancer. They are also classified as human carcinogens (known or probable) according to the U.S. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance. Their toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals. Their multiple industrial, domestic, agricultural, medical and technological applications have led to their wide distribution in the environment raising concerns over their potential effects on human health and the environment. Heavy metals are naturally occurring elements that have a high atomic weight and a density at least 5 times greater than that of water. ![]()
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